Detachment mechanisms for implantable devices

ABSTRACT

Disclosed herein are detachment mechanisms for vaso-occlusive devices that allow for rapid operator-controlled release of the vaso-occlusive device into the selected site. Also disclosed are vaso-occlusive assemblies comprising these detachment mechanisms and methods of using these detachment mechanisms and vaso-occlusive assemblies.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/010,048, filed Jan. 4, 2008, the disclosure of whichis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

Compositions and methods for implanting devices are described. Inparticular, detachment mechanisms that change configuration to deploy animplantable device such as an embolic device and assemblies comprisingthese detachment mechanisms are described.

BACKGROUND

Implantable devices are used for many indications including in thereproductive tract (e.g., uterine artery, fallopian occlusion), billiaryimplants and/or for peripheral and neurovasculature indications. Forexample, an aneurysm is a dilation of a blood vessel that poses a riskto health from the potential for rupture, clotting, or dissecting.Rupture of an aneurysm in the brain causes stroke, and rupture of ananeurysm in the abdomen causes shock. Cerebral aneurysms are usuallydetected in patients as the result of a seizure or hemorrhage and canresult in significant morbidity or mortality.

There are a variety of materials and devices which have been used fortreatment of peripheral and neurovascular aneurysms, including platinumand stainless steel microcoils, polyvinyl alcohol sponges (Ivalone), andother mechanical devices. For example, vaso-occlusion devices aresurgical implements or implants that are placed within the vasculatureof the human body, typically via a catheter, either to block the flow ofblood through a vessel making up that portion of the vasculature throughthe formation of an embolus or to form such an embolus within ananeurysm stemming from the vessel. One widely used vaso-occlusive deviceis a helical wire coil having windings that may be dimensioned to engagethe walls of the vessels. (See, e.g., U.S. Pat. No. 4,994,069 toRitchart et al.). Variations of such devices include polymeric coatingsor attached polymeric filaments have also been described. See, e.g.,U.S. Pat. Nos. 5,226,911; 5,935,145; 6,033,423; 6,280,457; 6,287,318;and 6,299,627. In addition, coil designs including stretch-resistantmembers that run through the lumen of the helical vaso-occlusive coilhave also been described. See, e.g., U.S. Pat. Nos. 5,582,619;5,833,705; 5,853,418; 6,004,338; 6,013,084; 6,179,857; and 6,193,728.

Coils have typically been placed at the desired site within thevasculature using a catheter and a pusher. The site is first accessed bythe catheter (e.g., small diameter catheters such as those shown in U.S.Pat. Nos. 4,739,768 and 4,813,934). The catheter may be guided to thesite through the use of guidewires (see U.S. Pat. No. 4,884,579) or byflow-directed means such as balloons placed at the distal end of thecatheter.

Once the site has been reached, the catheter lumen is cleared byremoving the guidewire (if a guidewire has been used), and one or morecoils are placed into the proximal open end of the catheter and advancedthrough the catheter with a pusher. Once the coil reaches the distal endof the catheter, it is discharged from the catheter by the pusher intothe vascular site. However, there are concerns when discharging the coilfrom the distal end of the catheter. For example, the plunging action ofthe pusher and the coil can make it difficult to position the coil atthe site in a controlled manner and with a fine degree of accuracy.Inaccurate placement of the coil can be problematic because once thecoil has left the catheter, it is difficult to reposition or retrievethe coil.

Several techniques involving Interlocking Detachable Coils (IDCs), whichincorporate mechanical release mechanisms and Guglielmi Detachable Coils(GDCs), which utilize electrolytically actuated release mechanisms, havebeen developed to enable more accurate placement of coils within avessel.

Electrolytic coil detachment is disclosed in U.S. Pat. Nos. 5,122,136;5,354,295; 6,620,152; 6,425,893; and 5,976,131, all to Guglielmi et al.,describe electrolytically detachable embolic devices. U.S. Pat. No.6,623,493 describes vaso-occlusive member assembly with multipledetaching points. U.S. Pat. Nos. 6,589,236 and 6,409,721 describeassemblies containing an electrolytically severable joint. The coil isbonded via a metal-to-metal joint to the distal end of the pusher. Thepusher and coil are made of dissimilar metals. The coil-carrying pusheris advanced through the catheter to the site and a small electricalcurrent is passed through the pusher-coil assembly. The current causesthe joint between the pusher and the coil to be severed viaelectrolysis. The pusher may then be retracted leaving the detached coilat an exact position within the vessel. Since no significant mechanicalforce is applied to the coil during electrolytic detachment, highlyaccurate coil placement is readily achieved. In addition, the electriccurrent may facilitate thrombus formation at the coil site. Thedisadvantage of this method is that the electrolytic release of the coilmay require a period of time that may inhibit rapid detachment of thecoil from the pusher.

There is a need to provide alternative mechanisms for deliveringimplants, such as embolic coils, that allow for both accuratepositioning of the implantable device and rapid detachment from thedelivery device.

SUMMARY

Disclosed herein are detachment mechanisms for implantable devices, aswell as assemblies comprising the detachment mechanisms and implantabledevices. Methods of making and using these detachment mechanisms andassemblies are also provided.

In one aspect, provided herein is a detachment mechanism for animplantable device, the implantable device optionally having a lumentherein, the detachment mechanism comprising: at least one material thatchanges configuration upon application of heat or electrical energy,wherein the change in configuration releases the implantable device, andfurther wherein if the material extends into the optional lumen of theimplantable device, the material directly contacts at least a portionthe implantable device defining the lumen. Thus, if the material extendsinto the lumen of the device, the material is in direct contact with theinterior surface of the implantable device. In certain embodiments, thechange in configuration comprises a reduction in diameter and/or volumeof the material. In other embodiments, the change in configurationcomprises an expansion in diameter and/or volume of the material. Instill other embodiments, the change in configuration comprises adeflection of the detachment mechanism.

In certain aspects, the detachment mechanisms described herein comprisean electroactive polymer and/or a metal or polymer, for example theelectroactive polymer may be layered onto the metal or polymer.

In other aspects, the detachment mechanisms described herein comprise alayered strip of two or more metals of dissimilar thermal coefficients.In certain embodiments, the layered strip is wound into a spiral shape.

In any of the detachment mechanisms described herein, the material maydirectly contacts a source of electric or heat energy. Furthermore, anyof the detachment mechanisms described herein may directly engage thevaso-occlusive device. In addition, the detachment mechanism maycontacts a structure attached to the implantable device.

In another aspect, described herein is a detachment mechanism adapted todetachably engage a vaso-occlusive device, the detachment mechanismcomprising an element that changes configuration upon application ofelectrical current or heat; and means for applying electrical current orheat to the change the configuration of the element.

In yet another aspect, provided herein is a vaso-occlusive assemblycomprising a vaso-occlusive device; any of the detachment mechanismsdescribed herein; and a source of electrical current or a heat source incontact with the detachment mechanism. In certain embodiments, thevaso-occlusive device comprises a helically wound vaso-occlusive coil.In still further embodiments, the vaso-occlusive assembly may furthercomprise a delivery mechanism, for example, a delivery mechanismcomprising a stopper element.

In a still further aspect, described herein is a method of at leastpartially occluding an aneurysm, the method comprising the steps ofintroducing any of the vaso-occlusive assemblies described herein intothe aneurysm, wherein the detachment mechanism engages thevaso-occlusive device; and changing the configuration of the detachmentmechanism by applying or removing electrical current or thermal energysuch that the detaching mechanism releases the vaso-occlusive deviceinto the aneurysm.

These and other embodiments will readily occur to those of skill in theart in light of the disclosure herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a partial cross-section, side view depicting an exemplaryvaso-occlusive assembly as described herein. The electroactive polymeris shown in the configuration in which it engages the vaso-occlusivedevice to be delivered.

FIG. 2 is a partial cross-section, side view depicting the exemplaryvaso-occlusive assembly of FIG. 1 and showing the electroactive polymerdetachment mechanism in the configuration that does not engage thevaso-occlusive device.

FIG. 3, panels A, B and C, are partial cross-section, side viewsdepicting another exemplary vaso-occlusive as described herein, in whichthe electroactive polymer extends beyond the distal end of the deliverydevice. FIG. 3A shows such an assembly when the electroactive polymerengages the vaso-occlusive device. FIG. 3B shows the assembly of FIG. 3Aupon changing the configuration of the polymer to increase the lengthand reduce thickness of the polymer. FIG. 3C shows an intermediatede-energized state, which allows the delivery device to function as acoil pusher.

FIG. 4 is a cross-section, side-view of yet another exemplary assemblyas described herein and shows a variation in which a structural elementis attached to the distal end of the vaso-occlusive device to engage theelectroactive polymer in one configuration and which, in the secondconfiguration, releases the structure and, accordingly, thevaso-occlusive device.

FIG. 5 is a cross-section, side-view of yet another exemplary assemblyas described herein and shows a design having two (inner and outer)layers of electroactive polymer.

FIG. 6, panels A to F, are cross-sections of exemplary configurationsshowing layering of electroactive polymer, filler material and corematerial, with or without slots.

FIG. 7 is a cross-section, side-view of an exemplary assembly asdescribed herein including a delivery device with one or more aperturesin the sidewalls.

FIG. 8 is a cross-section view of an exemplary electroactive polymerconfiguration that includes apertures (pores) in the electroactivepolymer.

FIGS. 9A and 9B are cross-section views of additional exemplaryelectroactive polymer configurations. FIG. 9A shows an embodiment thatincludes slots in the electroactive polymer. FIG. 9B shows a ring shapedelectroactive polymer with channels in the outer layer.

FIG. 10, panels A and B, are partial cross-section, side views depictingan exemplary assembly as described herein comprising an electroactivepolymer that contracts upon activation with electrical current. FIG. 10Ashows the assembly when electric current is applied to the electroactivepolymer, which contracts to release the embolic coil. FIG. 10B shows theassembly in the un-activated in which the electroactive polymer is in anexpanded configuration that engages the embolic coil.

FIG. 11, panels A and B, are partial cross-section, side views ofanother exemplary embodiment in which the electroactive polymer is in anexpanded configuration upon activation with electrical current. FIG. 11Ashows the assembly in the activated (engaged) configuration and FIG. 11Bshows contraction of the electroactive polymer in the un-activatedconfiguration (when electrical current is removed).

FIG. 12, panels A and B, are overviews of a bi-layered strip ofmaterials where each layer responds differently to the application ofelectrical current or heat. FIG. 12A shows an exemplary strip prior toapplication of heat or electrical current. FIG. 12B shows dissimilarexpansion of the disparate layers upon application of heat or electricalcurrent.

FIG. 13, panels A and B, are overviews of a bi-layered strip used indetachment mechanisms as described herein. FIG. 13A shows the bi-layerstrip prior to application of heat or electrical current. FIG. 13B showsdeflection of the strip upon application of heat or electrical currentdue to the dissimilar thermal and/or electrical response characteristicsof the layers.

FIG. 14, panels A and B are cross-section views of an exemplarydetachment mechanism comprising a bilayer strip as shown in FIGS. 12 and13 wound into a spiral shape and inserted into the lumen of animplantable device. FIG. 14A shows the strip in the unengaged position.FIG. 14B shows the strip when engaged with the inner surface of thelumen of the implantable device.

FIG. 15 is a cross-section view of an exemplary detachment mechanismcomprising bilayer strips extending into the lumen of the implantableembolic coil and contacting the inner surface of the embolic coil. Thestrips are shown in the configuration in which they engage spaces in thewinds of the embolic coil.

FIG. 16 is a cross-section view of the exemplary detachment mechanism ofFIG. 15 shown in the configuration in which they deflect toward eachother and no longer engage the coil.

FIG. 17 is a cross-section, side-view of an exemplary assembly asdescribed herein including a delivery device.

FIG. 18 is a cross-section, side-view of an exemplary assembly asdescribed herein including a delivery device with one or more aperturesin the sidewalls.

FIG. 19 is a partial cross-section, side view depicting an exemplaryvaso-occlusive assembly comprising an electroactive polymer plug in thedelivery device. The electroactive polymer plug is shown in the reducedconfiguration in which the distal boundary of the plug is proximal tothe distal end of the delivery device.

FIG. 20 is a partial cross-section, side view depicting the exemplaryvaso-occlusive assembly of FIG. 19 and shows the electroactive polymerplug in the expanded configuration in which the distal boundary of theplug is at or near the distal end of the delivery device, therebyextruding the vaso-occlusive device into the selected site.

FIG. 21 is a partial cross-section, side view depicting an exemplaryvaso-occlusive assembly as described herein. The delivery deviceincludes a collar that is sized to allow for the passage of thevaso-occlusive device. The electroactive polymer plug is shown in thereduced configuration in which the distal boundary of the electroactivepolymer plug is proximal to the distal end of the delivery device andcollar.

FIG. 22 is a partial cross-section, side view of the assembly shown inFIG. 21 with the electroactive polymer plug in the expandedconfiguration which causes the plug to extend into the collar andextrude the vaso-occlusive device from the delivery mechanism.

FIG. 23 is a cross-section, side-view of another exemplary assembly asdescribed herein and shows a design having apertures in the proximalstopper to allow flow of electrolytes to the electroactive polymer.

FIG. 24 is a cross-section, side-view of the exemplary assembly shown inFIG. 23 and further depicting a delivery device with one or moreapertures in the sidewalls.

FIG. 25, panels A to C, are side-views showing an exemplary variation inwhich a detachment mechanism comprising an electroactive polymer isattached to a structure on the proximal end of the implantable device.In the unexpanded configuration, the electroactive polymer engages thestructure and in the expanded configuration releases the structure anddeploys the implantable device.

FIG. 26, panels A and B, are cross-section, side-views showing anexemplary variation in which the implantable device engages a pusherelement when the electroactive polymer is in the contracted position.FIG. 26B depicts how, upon expansion of the electroactive polymer, theimplantable device is released.

FIG. 27, panels A to D, are cross-section showing an exemplary variationin which the implantable device engages a pusher element via a ringshaped electroactive polymer. FIG. 27A shows the electroactive polymerring in the engaged (unexpanded) configuration and FIG. 27B shows linearexpansion of the electroactive polymer ring which releases the ring fromthe pusher element. FIG. 27C shows an electroactive polymer ringstructure made of multiple linearly-expanding elements in an unexpandedconfiguration and FIG. 27D shows the ring of FIG. 27C after linearexpansion of the electroactive polymer elements.

FIG. 28, panels A and B, are cross-section, side-views showing anotherexemplary variation in which the implantable device engages a pusherelement via a ball joint when the electroactive polymer is in thecontracted position (FIG. 28A). Upon expansion of the electroactivepolymer, the implantable device is released (FIG. 28B).

FIG. 29, panels A and B, are cross-section, side-views showing anotherexemplary variation in which the implantable device engages a pusherelement via arms through a ring structure when the electroactive polymeris in the contracted position. Upon expansion of the electroactivepolymer, implantable device is released.

FIGS. 30, panels A to D, show an embodiment where the unexpandedelectroactive polymer engages an implantable coil and pusher element viaa structure extending from the proximal end of the coil. FIG. 30A is across-section side-view of the assembly with the electroactive polymerin the unexpanded position. FIG. 30B is a cross-section, side-view ofthe assembly with the electroactive polymer in the expanded position.FIG. 30C is a top view of the structure extending from the implantablecoil and electroactive polymer in unexpanded configuration. FIG. 30D isa top view of the structure shown in FIG. 30C with the electroactivepolymer in the expanded configuration.

FIG. 31, panels A and B, show a variation including an electroactivepolymer coupling receiver in which the structure extending from theimplantable device is engaged in the coupling receiver when theelectroactive polymer is in the expanded configuration (FIG. 31A) andwhich releases the implantable device when the electroactive polymer isin the unexpanded configuration (FIG. 31B).

FIG. 32, panels A and B, show an electroactive polymer activatedcompression (e.g., hydraulic) detachment mechanism. FIG. 32A shows theassembly when the electroactive polymer is in the unexpandedconfiguration and FIG. 32B shows the same assembly after expansion ofthe electroactive polymer.

FIG. 33, panels A and B, are cross-section, side-views showing anotherexemplary variation in which the implantable device engages a T-barstructure when the electroactive polymer is in the contracted position(FIG. 33A). Upon expansion of the electroactive polymer, the implantabledevice is released (FIG. 33B).

FIG. 34, panels A and B, are cross-section, side-views showing anotherexemplary variation in which the implantable device engages a T-barstructure when the electroactive polymer is in the contracted position(FIG. 34A). Upon expansion of the electroactive polymer, the implantabledevice is released (FIG. 34B).

FIG. 35, panels A and B, are cross-section, side-views showing anotherexemplary variation in which the implantable device includes a proximalball structure which is engaged in the delivery device by theelectroactive polymer in an expanded position (FIG. 35A). Uponcontraction of the electroactive polymer, the implantable device isreleased (FIG. 35B).

DETAILED DESCRIPTION

Detachment mechanisms for implantable devices, including occlusive(e.g., embolic) devices, and assemblies are described. The detachmentmechanisms described herein can be utilized in devices useful invascular and neurovascular indications and are useful in deliveringembolic devices to aneurysms, for example small-diameter, curved orotherwise difficult to access vasculature, for example aneurysms, suchas cerebral aneurysms. Methods of making and using these detachments andassemblies comprising these detachments are also aspects of thisdisclosure.

Currently, the gold-standard method of delivering implantablevaso-occlusive devices is via electrolytic detachment (e.g., GDC coils).While electrolytic detachment solves the drawbacks of earlier mechanicaldetachments (e.g., the need for the mechanism to be fully inside thecatheter in order to remain engaged), electrolytically detachable coilstypically require approximately 20-30 seconds detachment times.

The detachment mechanisms described herein that allow for rapid andprecise detachment of an implantable device upon application ofelectrical energy and/or heat. Advantages of the present disclosureinclude, but are not limited to, (i) the provision of rapidly detachablevaso-occlusive devices; (ii) the provision of mechanically detachableimplantable devices that can be extended beyond the catheter tip,thereby allowing for more precise placement of the devices; and (iii)the provision of occlusive devices that minimize the mechanical motionneeded to detach the devices.

All publications, patents and patent applications cited herein, whetherabove or below, are hereby incorporated by reference in their entirety.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the content clearly dictates otherwise. Thus, for example,reference to a device comprising “an electroactive polymer” includesdevices comprising of two or more such materials or multiple layers ofthe same electroactive polymer.

The detachment mechanisms described herein allow for rapid release ofthe vaso-occlusive device from the delivery mechanism. By “rapid”release is meant release in less than 30 seconds, preferably less than20 seconds and even more preferably between 1 and 15 seconds (e.g., 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 seconds).

The detachment mechanism may take any desired shape. The detachmentmechanism may engage the implantable device by contacting the exteriorof the device, directly (e.g., the exterior of the device) or indirectly(e.g., via a structure in contact with the exterior of the device).However, unlike previously described electroactive detachment mechanismsfor implantable devices, when the detachment extends into the lumen ofthe implantable device, it directly engages the interior surface of thedevice (in either the activated or inactivated state, depending on theproperties of the selected materials). The detachment mechanism may beshaped into a ring or spiral structure, for example a spiral wound froma bilayer strip.

In certain aspects, the detachment mechanism comprises an electroactivepolymer (EAP) that changes configuration upon the application toelectrical energy. Any electroactive polymer can be used, so long as itchanges configuration sufficiently in response to application ofcurrent. Multiple electroactive polymers may be used, for example, inlayers and/or admixed together. Non-limiting examples of suitableelectroactive polymers include polypyrrole, nafion, polyanilene,polythiofene and the like. See, e.g., U.S. Pat. No. 6,933,659 and U.S.Patent Publication 20040182704. Electroactive polymers may expand orcontract upon activation.

In certain embodiments, the change in configuration of the electroactivepolymer(s) is such that, upon the application of electrical current, thepolymer's diameter is reduced and, optionally, the axial length isincreased. Thus, in the absence of electrical current, the detachmentmechanism engages the implantable device within the delivery device.This allows that the delivery-detachment mechanism and vaso-occlusivedevice to be moved as a unit, even when the implantable device issecured by the electroactive polymer such that extends from the distalend of the delivery mechanism (e.g., delivery catheter or deliverytube). When electricity is applied, the electroactive polymer changesconfiguration (contracts) such that it no longer secures the device tothe delivery device. Accordingly, upon application of electricity to thedevice is rapidly released into the selected site. In these embodiments,the unactivated electroactive polymer provides a physical compressivegrip on the implantable device (e.g., on the exterior or interiorsurface and/or on a structure affixed to the proximal end of theimplantable device) until electrical current is used to active thedetachment mechanism. These “fail safe” embodiments minimize thepossibility of false or premature detachment of the coil and areadvantageous in the event of power failure or accidental interruption sothat the embolic remains attached to the delivery wire.

Alternatively, the electroactive polymer may be such that its diameterincreases upon application of electrical current. In these embodiments,electrical energy would be applied during deployment and release of theimplantable device achieved by stopping the application of electricalcurrent when the implantable device is in the desired position. Inembodiments in which the electroactive polymer expands upon theapplication of electrical energy, the implantable device is positionedwithin the delivery device and the electroactive polymer is energized tokeep the coil in the desired position. The device is then introducedinto the access delivery device (e.g., microcatheter). Upon achievingthe desired positioning within the aneurysm, the coil is detached byde-energizing the electroactive polymer. These embodiments allow theoption of the supplying long lengths of uncut embolic coils to thesurgeon. The surgeon can trim the coils to the desired length and mountthem on the delivery device to deploy the coils. Delivery devices can bereused multiple times so long as the lumen remains sufficiently clearfor insertion.

Detachment mechanisms comprising an electroactive polymer may furthercomprise metal (e.g., nitinol, stainless steel) and/or polymericmaterials. In certain embodiments, the detachment mechanism comprises asuper-elastic metal alloy such as nitinol which allows for durabilityand flexibility. Stainless steel or other metals or alloys can also beused. A portion or all of the detachment mechanism may include one ormore surface treatments (coating, machining, microtexturing, etc.). Theelectroactive polymer is typically coated onto the surface of the metaland/or polymeric material.

In other embodiments, the detachment mechanism comprises two or morematerials (e.g., metals and/or polymers), typically in layers.Furthermore, in response to thermal or electrical energy, the two ormore materials of the detachment mechanism change configurationdifferently. For example, in certain embodiments, the detachmentmechanism comprises a bilayer strip of an electroactive polymer coatedonto a metal or polymer substrate. In other embodiments, metals orpolymers that respond differently when activated by thermal orelectrical energy are employed. The detachment mechanisms describedherein also allow for ready retrieval and/or repositioning ofvaso-occlusive devices.

Suitable delivery devices include delivery catheters (e.g.,microcatheters) with or without delivery tubes (hypotubes) therein. Whenincludes, hypotubes may extend the length of the delivery catheter ormay be only at the distal region. The delivery devices may include oneor more apertures in the side walls that allow for inflow and outflow ofelectrolytes. See, also, U.S. Provisional Patent Application No.60/930,436, entitled “Catheters for Electrolytically Detachable EmbolicDevices,” filed May 16, 2007. In any of the embodiments describedherein, the delivery device may be slotted or spiral cut to reducebending stiffness while maintaining axial controllability.

In certain embodiments, a braided delivery tube, for example comprisingelectrodes or heat conducting elements embedded in the sidewalls orextending through the lumen of the delivery tube is employed. Suchdelivery tubes are adapted to be delivered through conventionalcatheters (e.g., microcatheters) and, when extended from the distal endof the catheter, allow for even more accurate positioning of theimplantable device prior to detachment. In other embodiments, theelectrodes (bi-polar or unipolar) extend through the part or all of thelumen of the delivery device.

Furthermore, as noted above, electrical or thermal energy can beprovided to the detachment mechanism in any suitable way. The energysource can directly contact the detachment mechanism, for example usinga delivery mechanism (e.g., catheter or delivery tube) comprisingelectrodes or heat conductors in the side-walls. See, e.g., U.S. Pat.Nos. 6,059,779 and 7,020,516. In addition, the electrodes can beattached to a core wire. For example, bi-polar electrodes and/or anodesalone or twisted with a core wire cathode can also be used to supplycurrent to the electroactive polymer. Optionally, the leads may besecured to the core wire, for example via adhesives or via heat-shrinkpolymer lamination such as PTFE, FEP, PET or urethane. The conductiveelement may include a polymer jacket/liner to insulate the electricalleads and/or reduce friction during advancement. Alternatively, thedetachment mechanism can be activated to change configuration indirectlyvia a conductive material (e.g., metal) that transmits the electrical orthermal energy to the detachment junction.

It will be apparent that one or more of the electrodes and/or conductivematerials that transmit electrical energy to the electroactive polymermay include insulating coatings (e.g., polyimide or the like). Forelectrical energy, alternating or direct current may be used.Preferably, direct current is used. The amount of current applied willvary according to the application although typically less than 4 volts,preferably around 2 volts is applied to activate the electroactivepolymer of the detachment mechanism. Likewise, for materials that changeconfiguration in response to thermal energy, heat can be applied asdesired by the operator to change the configuration of the detachmentmechanism.

In certain embodiments, the conductor and/or electrodes are distal tothe distal end of the delivery mechanism (e.g., tube or coil stopper).As shown in the Figures, the detachment mechanism may be disposed overthe conductive surfaces, for example by physical expansion over theelectrodes/heat conductors, heat shrinking, conductive adhesives, or thelike.

The detachment mechanisms described herein can be adapted to be usedwith any implantable device, including, but not limited to,vaso-occlusive devices, fallopian tube occlusive devices, uterineimplantable devices, billiary implantable devices and the like. Thedevices may be metal and/or polymeric. Suitable metals and metal alloysinclude the Platinum Group metals, especially platinum, rhodium,palladium, rhenium, as well as tungsten, gold, silver, tantalum, andalloys of these metals. The core element may also comprise of any of awide variety of stainless steels. Very desirable materials ofconstruction, from a mechanical point of view, are materials thatmaintain their shape despite being subjected to high stress includingbut not limited to “super-elastic alloys” such as nickel/titanium alloys(48-58 atomic % nickel and optionally containing modest amounts ofiron); copper/zinc alloys (38-42 weight % zinc); copper/zinc alloyscontaining 1-10 weight % of beryllium, silicon, tin, aluminum, orgallium; or nickel/aluminum alloys (36-38 atomic % aluminum).Particularly preferred are the alloys described in U.S. Pat. Nos.3,174,851; 3,351,463; and 3,753,700. Especially preferred is thetitanium/nickel alloy known as “nitinol.”

The detachment mechanisms described herein may be used with implantabledevices of any structure, for example, devices of tubular structures,for examples, braids, coils, combination braid and coils and the like.Thus, although depicted in the Figures described below as avaso-occlusive coil, the device may be of a variety of shapes orconfiguration including, but not limited to, braids, knits, wovenstructures, tubes (e.g., perforated or slotted tubes), cables,injection-molded devices and the like. See, e.g., U.S. Pat. No.6,533,801 and International Patent Publication WO 02/096273. Theimplantable device may change shape upon deployment, for example changefrom a constrained linear form to a relaxed, three-dimensional(secondary) configuration. See, also, U.S. Pat. No. 6,280,457. In apreferred embodiment, the core element comprises a metal wire wound intoa primary helical shape. The core element may be, but is notnecessarily, subjected to a heating step to set the wire into theprimary shape. Methods of making vaso-occlusive coils having a linearhelical shape and/or a different three-dimensional (secondary)configuration are known in the art and described in detail in thedocuments cited above, for example in U.S. Pat. No. 6,280,457. Thus, itis further within the scope of this disclosure that the vaso-occlusivedevice as a whole or elements thereof comprise secondary shapes orstructures that differ from the linear coil shapes depicted in theFigures, for examples, spheres, ellipses, spirals, ovoids, figure-8shapes, etc. The devices described herein may be self-forming in thatthey assume the secondary configuration upon deployment into ananeurysm. Alternatively, the devices may assume their secondaryconfigurations under certain conditions (e.g., change in temperature,application of energy, etc.).

FIG. 1 shows a partial cross-section, side-view of an exemplarydetachable vaso-occlusive assembly as described herein in aconfiguration in which the electroactive polymer engages thevaso-occlusive device within delivery device. In this position, theelectroactive polymer 20 engages the proximal region of vaso-occlusivecoil 10, namely tip ball 15 of the vaso-occlusive coil 10. Electrodes40, 45 extend through sidewall of delivery tube 30 and contactelectroactive polymer 20. For electroactive polymers that contract uponapplication of electrical current, FIG. 1 shows the assembly in theun-activated state, where the electroactive polymer creates a lumenhaving an inner diameter (ID) smaller than the outer diameter (OD) ofthe embolic coil, allowing it to hold the coil in place. Forelectroactive polymers that expand upon application of electricalcurrent, FIG. 1 shows the assembly in the activated state, again holdingthe coil in place.

FIG. 2 is a side and partial cross-section view of the vaso-occlusiveassembly of FIG. 1 after changing configuration of the electroactivepolymer by application or removal of electrical current. Forelectroactive polymers that contract upon application of electricalenergy, hydration and ion transport around the electroactive polymershrinks the polymer, thereby reducing its thickness. Likewise, forelectroactive polymers that expand upon application of electricalenergy, the polymer will contract when the electrical current isremoved. In either case, the shrunken polymer 20 releases its hold onthe coil 10, and allows withdrawal of the delivery device 30 whileleaving the coil 10 in the vessel.

FIG. 3, panels A to C, show another exemplary assembly in which theelectroactive polymer material 20 extends beyond the delivery device 30.FIG. 3A shows a cross-section of the assembly in the engagedconfiguration. FIG. 3B is a cross-section view of the embodiment of FIG.3A upon changing the configuration of the electroactive polymer byapplication or removal of electrical energy. The inner diameter of thetube created by the electroactive polymer 20 increases and, in addition,the axilinear length of the polymer increases. This minimizes coilmovement during detachment. FIG. 3C shows the detachment mechanism in anintermediate activated state in which the thickness of the electroactivepolymer 20 is partially shrunk and the polymer can aid in coil 10positioning and/or pushing.

FIG. 4 shows an exemplary embodiment in which a structural element (e.g.ball) 70 is secured at or near the proximal end of the coil 10 andextends through the electroactive polymer 20. The ball 70 is placedinside the delivery tube and held in place by the electroactive polymer20. When the configuration of the electroactive polymer 20 is changedvia anode 75 and cathode 77, the electroactive polymer 20 changesconfiguration sufficiently to produce a luminal gap large enough for thedelivery tube to be withdrawn over the ball 70. This design may provideimproved tensile strength because the tensile load surface is loadednormally instead of in shear.

It will be apparent that the structure may be secured to the coil at anylocation and by any suitable means, for example, gluing, soldering,welding, etc. Furthermore, any structural element can be used,including, for example, ball, rings, hooks and the like.

FIG. 5 shows yet another design using multiple layers of electroactivepolymer 20. In this design, the inner and outer surfaces of the proximalend of the coil 10 are surrounded by electroactive polymer 20. Alsoshown are delivery tube 30, anodes 75, and cathodes 77.

FIG. 6A to 6F are cross-section views of detachment mechanismscomprising an electroactive polymer and additional materials. Shown inFIG. 6 are configurations in which the electroactive polymer is layeredwith other materials that fill space and/or provide desirable adhesionproperties to the delivery device or coil. Other configurations, forexample, mixtures of materials and overlapping regions of differentmaterials are also contemplated. Non-limiting examples of othermaterials include metal and/or polymers (e.g., PET).

FIGS. 6A to 6C depict embodiments in which the electroactivepolymer-comprising structure is a ring or tube-like shape. FIG. 6A showsa cross-section view of an exemplary detachment mechanism including aninner electroactive polymer inner layer 20, an outer core (e.g., tube)layer 85 and a middle layer of filler polymer 80 sandwiched between theelectroactive polymer 20 and the outer tube layer 85. FIG. 6B shows across-section view of another exemplary detachment mechanism includingan inner filler polymer layer 80, an outer tube layer 85 and a middlelayer of electroactive polymer 20 sandwiched between the filler polymer80 and the outer core layer 85. FIG. 6C shows a cross-section view ofanother exemplary detachment mechanism including an inner electroactivepolymer layer 20, an outer core or tube layer 85 and a middle layer offiller material 85 sandwiched between the electroactive polymer 20 andthe outer core layer 85. FIG. 6C also illustrates how the detachmentmechanism need not be a solid annulus, but can include one or more slots87 or other discontinuous formations that may allow for more uniformand/or facile expansion and contraction of the electroactive polymer.

FIGS. 6D through 6F depict embodiments in which detachment mechanismcomprises a core wire instead of tube. In particular, FIG. 6D shows across-section view of an exemplary detachment mechanism comprising acore wire 85 surrounded by a layer of filler material 80, which in turnis surrounded by an outer layer of electroactive polymer 20. FIG. 6Eshows the detachment mechanism of FIG. 6D further comprising slots 87 inthe electroactive polymer 20 and filler material layers 80. FIG. 6Fshows a cross-section view of an exemplary detachment mechanismcomprising a core wire 85 surrounded by a layer of electroactive polymer20, which in turn is surrounded by an outer layer of filler material 80.Also shown are slots 87 in the electroactive polymer 20 and fillermaterial layers 80.

FIG. 7 shows a cross-section view of an exemplary assembly describedherein in which the deployment tube 30 comprises one or more apertures95 in the sidewalls of the delivery tube. Also shown are electroactivepolymer 20, which forms a ring in the inside of the delivery tube 30,electrodes 90 and implantable device 10. The apertures in the sidewallsallow for both inflow of electrolytes (e.g., blood) and outflow ofelectrolytes that can be infused into the lumen of the delivery deviceby the operator. Non-limiting examples of suitable electrolytes includesaline, phosphate buffered saline and the like.

FIGS. 8 and 9 show exemplary cross-section views of electroactivepolymer 20 configurations included apertures or slots 97 therein. Theuse of non-solid electroactive polymers provides more surface area forthe diffusion of electrolytes which further increases the efficiency ofthe applied electrical energy in changing the configuration of thepolymer and releasing the implantable device.

FIG. 10A is a side, cross-section view of an exemplary vaso-occlusiveassembly in which a detachment mechanism comprising a ring-shapedelectroactive polymer 20 disposed to fit within the lumen of theimplantable embolic coil 10 and mounted on the distal end of dualconductor electrode 32, with positive 35 negative 37 electrodes withinelectroactive polymer ring 20. The dual conductor electrode 32, may becoaxial or a twisted pair of conductors. Also shown in FIG. 10A ismarker coil 50, including radio-opaque (e.g., platinum) proximal coilwinds 55. The electroactive polymer 20 expands upon application ofelectrical current and is shown in the un-activated state in which ithas a diameter less than the inner diameter of the embolic coil 10.

FIG. 10B shows the assembly of FIG. 10A in the activated state. Thediameter of the electroactive polymer 20 increases upon application ofelectrical energy to hold the coil 10 in place, for example against astopper and/or marker coil 50.

When the delivery device comprises a marker or stopper coil, it can beof the same or different diameter than the implantable device. Incertain embodiments, the stopper coil has a slightly smaller innerdiameter than the implantable coil such that when the coils are axiallyaligned they contact each other but create a ridged area at theirjunctions. In the engaged position, the electroactive polymer expands togrip the uneven surface more firmly than if the coils were of the samediameter.

In embodiments in which the electroactive polymer expands upon theapplication of electrical energy, the implantable device is positionedwithin the delivery device and the electroactive polymer is energized tokeep the coil in the desired position. For example, in the design shownin FIG. 10, the electroactive polymer ring is inserted into the lumen ofthe main coil and energized. The device is then introduced into theaccess delivery device (e.g., microcatheter). Upon achieving the desiredpositioning within the aneurysm, the coil is detached by de-energizingthe electroactive polymer. These embodiments, allows the option of thesupplying long lengths of uncut embolic coils to the surgeon. Thesurgeon can trim the coils to the desired length and mount them on thedelivery device to deploy the coils. Delivery devices can be reusedmultiple times so as the lumen remains sufficiently clear for insertion.Furthermore, these embodiments minimize the possibility of false orpremature detachment of the coil.

FIG. 11 shows another embodiment in which the electroactive polymershrinks (reduces diameter) upon application of electrical current. FIG.11A is a side, cross-section of an exemplary vaso-occlusive assembly inan un-activated (expanded) state. A detachment mechanism comprising anelectroactive polymer 20 is disposed to fit within the lumen of theimplantable dual diameter embolic coil 10 and mounted on the distal endof dual conductor electrode 32, with positive 35 negative 37 electrodes.The dual conductor electrode 32, may be coaxial or a twisted pair ofconductors. Also shown in FIG. 11A is marker coil 50, includingradiopaque (e.g., platinum) proximal coil winds 55 and stopper bands 57.FIG. 11B shows the assembly of FIG. 11A in the activated state. Thediameter of the electroactive polymer 20 decreases upon application ofelectrical energy to release the embolic coil 10 into the desiredlocation in the vessel.

FIGS. 12 and 13 show side views of still other exemplary embodiments inwhich the detachment mechanism 70 is configured as a composite (layered)strip 60. FIG. 12A shows the composite strip in the release position andFIG. 12B shows the mismatch in expansion of the different layers in theactivated position. FIG. 13A shows the composite strip in the releaseposition and also shows a band 77 which may be used to keep the layersof the strip in contact. FIG. 13B shows the composite strip of FIG. 13Aupon activation (electrical current or heat) which causes differentdeflection of the layers of the strip.

FIG. 14A is front, cross-section view of a composite strip as shown inFIGS. 12 and 13 wound into a spiral shape and positioned within thelumen of an implantable coil 10 in the released configuration. FIG. 14Bshows the assembly of FIG. 14A in the engaged configuration, namely whenthe layered strip engages the inner surface of the implantable device20.

The layered strip may include an electroactive polymer which expands orcontracts upon application of electrical energy. Alternatively, thestrip may be comprised of two or more dissimilar metals having disparatethermal expansion coefficients such that, upon a change in temperature,they change shape with relation to the other(s), i.e. deflect, bend,and/or expand. It will be apparent that when an electroactive polymer isused in these strips, the detachment mechanism is operably liked to asource of electrical current. Likewise, is dissimilar metals are used,the strips are operably connected to a heat source.

FIG. 15 depicts a design using layered strips 60 as described above.FIG. 15 depicts a cross-section view of an embodiment in which compositestrips 60 extend through the lumen of marker coil 50 and into the lumenof the implantable embolic coil 10. In the expanded (engaged) positionthe strips 60 may engage the coil 10 directly (e.g., into the winds ofthe implantable coil) or, alternatively, may engage orifices (e.g.,gaps) or structures 80 positioned at appropriate locations within thecoil.

FIG. 16 shows yet another design using layered strips 60 within thelumen of an embolic coil 10 and which engage each other via interlockingelements 80 in the released configuration. As shown in FIG. 16, whenmultiple strips are used within the lumen of the implantable device,they may be offset from each other such that, when they are actuated,they pass each other, which may allow greater range of movement duringpositioning and deployment. For instance, the strips may be spacedequally around the lumen of implantable device (e.g., 180° apart for twostrips; 120° apart for 3 strips, etc.).

As noted above, in any of the embodiments described herein, there may beone or more layers of electroactive polymer. Furthermore, theelectroactive polymer can be deposited onto any substrate, for example ametal (e.g., nitinol) or polymer (e.g., urethane). The electroactivepolymer can be deposited by any means, for example by coating, gluing,and the like.

In certain embodiments, the assemblies described herein further comprisean element (e.g., band) around the proximal end of the implantabledevice and/or delivery mechanism to help maintain contact with theelectroactive polymer. Non-limiting examples of such elements includethin-walled metal (e.g., stainless steel, nitinol, and/or platinumalloys) and/or polymer (PEEK, PET, polyimide) bands. Alternatively, aregion of the coil (e.g., winds of the coil) can be soldered or weldedtogether.

FIG. 17 is a side, cross-section view of an exemplary vaso-occlusiveassembly in which a detachment mechanism comprising a ring-shapedelectroactive polymer 20 is disposed to fit within the lumen of theimplantable embolic coil 10 and mounted on the distal end of dualconductor electrode 32, with positive 35 and negative 37 electrodeswithin electroactive polymer ring 20. Also shown in FIG. 17 is markercoil 50, including radio-opaque (e.g., platinum) proximal coil winds 55and delivery device 90.

FIG. 18 is a side, cross-section view of an exemplary vaso-occlusiveassembly as shown in FIG. 17 in which the delivery device 90 includesapertures 95 in the sidewalls.

FIG. 19 shows a partial cross-section, side-view of another exemplarydetachable vaso-occlusive assembly as described herein which includes anelectroactive polymer plug 20 in the delivery tube 30. The electroactivepolymer plug 20 is shown in the reduced volume configuration andcontacts the proximal region (tip ball) of vaso-occlusive coil 10.Electrodes 40, 45 extend through sidewall of delivery tube 30 andcontact electroactive polymer 20. Delivery tube also comprises a stopper50 proximal to the electroactive polymer plug 20. Stopper 50 preventsexpansion of the electroactive polymer proximally within the deliverytube 30. For electroactive polymers that contract upon application ofelectrical energy, hydration, applied voltage from a power supply, andion transport around the electroactive polymer shrinks the polymer,thereby reducing the space it occupies in the delivery tube 30.

FIG. 20 is a side and partial cross-section view of the vaso-occlusiveassembly of FIG. 19 after the configuration of the electroactive polymerplug 20 is changed by application or removal of electrical current toits expanded configuration. The polymer plug 20 can expand only distallyin delivery tube 30 due to stopper 50 and, accordingly, when expandedpushes coil 10 out of the delivery device and allows withdrawal of thedelivery device 30 while leaving the coil 10 in the vessel.

FIG. 21 shows a partial cross-section, side-view of another exemplarydetachable vaso-occlusive assembly having an electroactive polymer plug20 and stopper 50. The electroactive polymer 20 is shown in the reducedvolume configuration and contacts the proximal region (tip ball) ofvaso-occlusive coil 10. Electrodes 40, 45 extend through sidewall ofdelivery tube 30 and contact electroactive polymer 20. Delivery tubealso comprises a stopper 50 proximal to the electroactive polymer 20.Delivery tube 30 includes a collar 35 that is sized to fit the outerdiameter of the vaso-occlusive coil 10.

FIG. 22 is a side and partial cross-section view of the vaso-occlusiveassembly of FIG. 21 after changing configuration of the electroactivepolymer plug 20 (by application or removal of electrical current) to itsexpanded configuration. The expanded polymer 20 pushes coil 10 out ofthe collar 35 of delivery device 30 and allows withdrawal of thedelivery device 30 while leaving the coil 10 in the vessel.

FIG. 23 shows yet another electroactive polymer plug type assembly asdescribed herein in which the stopper 50 comprises apertures 55. Theapertures allow electrolytes, for example electrolytic solutions thatare infused into the lumen of the delivery tube by the operator, tocontact the electroactive polymer 20.

FIG. 24 shows a cross-section view of an electroactive plug-typeassembly described herein in which the deployment tube 30 comprises oneor more apertures 95 in the sidewalls of the delivery tube. Also shownare electroactive polymer 20, stopper with apertures 50, 55, deliverytube 30, electrodes 90 and implantable device 10. The apertures in thesidewalls allow for both inflow of electrolytes (e.g., blood) andoutflow of electrolytes that can be infused into the lumen of thedelivery device by the operator. Non-limiting examples of suitableelectrolytes include saline, phosphate buffered saline and the like.

FIG. 25A shows a side view of another exemplary assembly as describedherein in which an electroactive polymer detachment mechanism 20 iswound around a structure 72 at the proximal end of the coil 10. Thedetachment mechanism 20 may optionally directly contact the coil 10.FIG. 25A shows the electroactive polymer 20 in the unexpanded (smallerdiameter) configuration in which the coil 10 is engaged by thedetachment mechanism 20. FIGS. 25B and 25C depict the device of FIG. 25Awith the electroactive polymer 20 in the expanded configuration which nolonger engages the structure 72, thereby releasing the coil 10. Asshown, the structure 72 engaged by the electroactive polymer 20 may beattached to the proximal end of the coil 10 (FIG. 25B) or to the distalend of a pusher element, for example a pusher comprising an electricalconductor 32.

Although shown in FIG. 25A-C as a coiled structure 72, it will beapparent that the electroactive polymer 20 may be attached to any shapedstructure, for example, a straight solid or hollow tube (optionallysurfaced roughened, e.g., by mechanical blasting, grinding or chemicaletching). It will also be apparent that the structure 72 may be made ofany material (polymer and/or metal), for example the same material asthe coil (e.g., platinum alloy). Likewise, the electroactive polymer maytake a variety of shapes, for example a ring shape or a helical (spiral)shape as depicted in FIG. 25. Optionally, the electroactive polymer maybe disposed on a substrate, for example a thin, flexible polymer such aspolyimide or polyester. In addition, one or more loops of the coil maybe soldered or welded together, which may reduce stretching duringmovement of the coil.

FIG. 26A shows a cross-section, side-view of an embodiment in whicharm-like structures 73 extending from the proximal region of the coil 10engage a pusher element 31 in slots containing an electroactive polymer20 in an unexpanded configuration. FIG. 26B shows the assembly when theelectroactive polymer 20 expands and the arms 73 no longer engage thepusher element 31. Pusher element 31 includes an electrical conductor 32for activation of the electroactive polymer 20.

The arms may be made of any material (e.g., polymer and/or metal) andmay be integral or attached to the implantable device. Although depictedin FIG. 26 with two arms, more than 2 arms may be employed and mayimprove tensile strength, for example, 3, 4, 5, 6 or even more arms. Thegrips may also be of any configuration that engages the arms and may bebuilt into the tubular pusher or may be attached to the distal end ofpusher. The pusher can be made from any material, for example nitinol.The pusher body may optionally comprise a metallic hypotube componentthat is flexible distally; a polymer jacket/liner; and/or a metalreinforced polymer structure. Additional elements, for example,radiopaque markers, may also be included on the pusher element.

FIG. 27A shows a cross-section, side-view of an embodiment in which theelectroactive polymer 20 is a ring attached to the proximal region ofthe coil 10 and which engages a pusher element 31 in the unexpandedconfiguration. FIG. 27B shows the assembly when the electroactivepolymer 20 expands and the diameter of the ring increases so it nolonger engages the pusher element 31 and the coil 10 is detached. Pusherelement 31 includes an electrical conductor 32 for activation of theelectroactive polymer 20 and optionally includes a slot or grooveadapted to fit the ring of electroactive polymer 20. FIG. 27C shows across-section of an exemplary electroactive polymer ring 20 may be madeup of multiple discontinuous electroactive polymer elements in anunexpanded state. FIG. 27D shows the electroactive polymer ringstructure 20 of FIG. 27C after linear expansion of the electroactivepolymer ring.

FIG. 28 to 30 show cross-section, side-views of additional embodimentsin which the implantable device 10 engages a pusher element 31 when theelectroactive polymer 20 is in a contracted position. FIG. 287A shows aball 73 structure on the proximal end of the coil 10 engaged by arms 74when the electroactive polymer 20 is contracted. FIG. 28B shows releaseof the ball joint when the electroactive polymer 20 is expanded. FIG.29A shows an assembly where arms 74 on the pusher element 31 engage aring structure 73 on the coil 10 when the electroactive polymer 20 is inthe contracted position. FIG. 29B shows the assembly when theelectroactive polymer 20 expands and the arms 74 no longer engage thering 73. FIG. 30A shows an assembly where the unexpanded electroactivepolymer 20 engages a structure 73, 73 a on the proximal end of the coil10 embodiment distal to the enlarged end 73 of the structure. FIG. 30Bshows the assembly upon expansion of the electroactive polymer 20 torelease the structure 73, 73 a and attached coil 10. FIG. 30C is a topview of the structure 73, 73 a extending from the implantable coil andelectroactive polymer 20 in unexpanded configuration and shows thepolymer 20 can be made into panels to promote radial expansion. FIG. 30Dis a top view of the structure shown in FIG. 30C with the electroactivepolymer panels in the expanded configuration.

FIG. 31 shows an embodiment that includes a coupling receiver 79extending from a delivery device 30. As shown in FIG. 31A, the couplingreceiver 79 comprises an electroactive polymer or electroactive strip(e.g. electroactive wire) 20 that engages a coupling device 73 extendingfrom the implantable device 10 when the electroactive polymer/strip 20is in an expanded configuration (e.g., activated). The electroactivepolymer 20 releases the coupling device 73 in the unexpanded (e.g.,deactivated). The coupling receiver 79 and coupling device 73 may be ofany configuration. Similarly, the electroactive polymer 20 may aring-like structure with or without channels therein, for example asshown in FIG. 9B. In other embodiments, the device includes anelectroactive wire, for example a nickel titanium shape memory orsuperelastic wire that responds to heat activation via electric current(see, also, FIGS. 12 and 13). Designs with a coupling mechanism mayenhance the ability of the operator to reposition and manipulate thedevice during implantation. For example, the delivery device anddetaching device may be able to rotate as much as 1 to 1 torque and/orindependent of each other.

FIG. 32 shows a compression (hydraulic) type detachment mechanismincluding a tubular pusher element made up of an incompressible material31 and an electroactive polymer 20. Typically, the incompressiblematerial 31 also acts as an electrolyte. The coil 10 is engaged with thetubular pusher element when the electroactive polymer is in theunexpanded configuration, for example by an interference fit. FIG. 32Ashows the assembly when the electroactive polymer 20 is in theunexpanded configuration. Upon volumetric expansion of the electroactivepolymer 20 the pressure inside the tubular pusher increases until thecoil 10 is released.

FIG. 33A shows a cross-section, side-view of an embodiment in which aT-bar structure 84 engages fin-like structures 87 attached to theimplantable coil 10. Also shown is an electrical conductor 32 foractivation of the electroactive polymer 20. Typically, the fin-likestructures 87 are attached to the implantable device (e.g., the interiorof a coil) and include apertures through which the T-bar structure 84extends. An electroactive polymer 20 is disposed on the T-bar 84 suchthat, in the contracted position, the T-bar 84 engages the fin-likestructures 87 extending from the implantable device 10. FIG. 33B showsthe assembly when the electroactive polymer 20 expands causing thefin-like structures 87 to extend beyond the ends of the T-bar 84 so thatthe T-bar 84 no longer engages the device 10.

FIGS. 34A and 34B show an alternative embodiment, in which the T-barstructure 84 is attached to the implantable device 10 and engagesstructures 87 proximal to the implantable device 10. As with theembodiment shown in FIG. 33, expansion of the electroactive polymer 20pushes the fins off the T-bar and releases the implantable device 10from the pusher element (FIG. 34B).

The T-bar may not be a single T in that any number of posts can be used,for example, 1, 2, 3, 4, 5 or even more posts can be used. In apreferred embodiment, the T-bar includes 2 posts.

Furthermore, the T-bar and structures (e.g., fin-like structures) itengages may be made of any material (e.g., polymer and/or metal). Incertain embodiments, the fin-like structures comprise platinum. In otherembodiments, the T-bar comprises platinum, nitinol, stainless steeland/or polyimide and can be electrochemically etched or formed bybending segments of wire. The fin-like structures or T-bar may beattached to the implant by any suitable means, including but not limitedto soldering, welding, adhesives, etc. An optional collar may be placedaround the finds and/or T-bar to reduce or prevent pivoting of the finsabout the T-bar structure.

FIG. 35 shows an exemplary embodiment in which a structural element(e.g. sphere or ovoid ball like structure) is secured at or near theproximal end of the coil 10 and into delivery device 30 (e.g., hypotube)where it is held in place by electroactive polymer 20 in an expandedconfiguration. When the polarity of current applied to the electroactivepolymer 20 is reversed via electrodes 32, the polymer expands linearlysuch that it no longer secures the device 10 within the delivery device30. Also shown is optional groove or slot in the delivery device 37 thatprovides a seating location of the proximal coil ball.

In any of the embodiments described herein, the electroactive polymer 20can be disposed directly on the delivery device or on a flexiblesubstrate 38, for example a flexible substrate that deflects when theelectroactive polymer 20 disposed therein is activated/unactivated byelectrical current (see, e.g., description above regarding FIGS. 13A andB).

The devices described herein are often introduced into a selected siteusing the procedure outlined below. This procedure may be used intreating a variety of maladies. For instance in the treatment of ananeurysm, the aneurysm itself will be filled (partially or fully) withthe compositions described herein.

Conventional catheter insertion and navigational techniques involvingguidewires or flow-directed devices may be used to access the site witha catheter. The mechanism will be such as to be capable of beingadvanced entirely through the catheter to place vaso-occlusive device atthe target site but yet with a sufficient portion of the distal end ofthe delivery mechanism protruding from the distal end of the catheter toenable detachment of the implantable vaso-occlusive device. For use inperipheral or neural surgeries, the delivery mechanism will normally beabout 100-200 cm in length, more normally 130-180 cm in length. Thediameter of the delivery mechanism is usually in the range of 0.25 toabout 0.90 mm. Briefly, occlusive devices (and/or additional components)described herein are typically loaded into a carrier for introductioninto the delivery catheter and introduced to the chosen site using theprocedure outlined below. This procedure may be used in treating avariety of maladies. For instance, in treatment of an aneurysm, theaneurysm itself may be filled with the embolics (e.g. vaso-occlusivemembers and/or liquid embolics and bioactive materials) which causeformation of an emboli and, at some later time, is at least partiallyreplaced by neovascularized collagenous material formed around theimplanted vaso-occlusive devices.

A selected site is reached through the vascular system using acollection of specifically chosen catheters and/or guide wires. It isclear that should the site be in a remote site, e.g., in the brain,methods of reaching this site are somewhat limited. One widely acceptedprocedure is found in U.S. Pat. No. 4,994,069 to Ritchart, et al. Itutilizes a fine endovascular catheter such as is found in U.S. Pat. No.4,739,768, to Engelson. First of all, a large catheter is introducedthrough an entry site in the vasculature. Typically, this would bethrough a femoral artery in the groin. Other entry sites sometimeschosen are found in the neck and are in general well known by physicianswho practice this type of medicine. Once the introducer is in place, aguiding catheter is then used to provide a safe passageway from theentry site to a region near the site to be treated. For instance, intreating a site in the human brain, a guiding catheter would be chosenwhich would extend from the entry site at the femoral artery, up throughthe large arteries extending to the heart, around the heart through theaortic arch, and downstream through one of the arteries extending fromthe upper side of the aorta. A guidewire and neurovascular catheter suchas that described in the Engelson patent are then placed through theguiding catheter. Once the distal end of the catheter is positioned atthe site, often by locating its distal end through the use of radiopaquemarker material and fluoroscopy, the catheter is cleared and/or flushedwith an electrolyte solution.

Once the selected site has been reached, the vaso-occlusive device isextruded using a pusher-detachment mechanism as described herein andreleased in the desired position of the selected site.

Modifications of the procedure and vaso-occlusive devices describedabove, and the methods of using them in keeping with this disclosurewill be apparent to those having skill in this mechanical and surgicalart. These variations are intended to be within the scope of the claimsthat follow.

1. A detachment mechanism for an implantable device, the detachmentmechanism comprising: at least one material that changes configurationupon application of heat or electrical energy, wherein the change inconfiguration releases the implantable device, and further wherein ifthe material extends into a lumen of the implantable device, thematerial directly contacts at least a portion the implantable device. 2.The detachment mechanism of claim 1, wherein the change in configurationcomprises a reduction in diameter and/or volume of the material.
 3. Thedetachment mechanism of claim 1, wherein the change in configurationcomprises an expansion in diameter and/or volume of the material.
 4. Thedetachment mechanism of claim 1, wherein the change in configurationcomprises a deflection of the detachment mechanism.
 5. The detachmentmechanism of claim 1, wherein the detachment mechanism comprises anelectroactive polymer.
 6. The detachment mechanism of claim 5, whereinthe detachment mechanism further comprises a metal or polymer andwherein the electroactive polymer is layered onto the metal or polymer.7. The detachment mechanism of claim 1, wherein the detachment mechanismcomprises a layered strip of two or more metals of dissimilar thermalcoefficients.
 8. The detachment mechanism of claim 7, wherein thelayered strip is wound into a spiral shape.
 9. The detachment mechanismof claim 1, wherein the at least one material that changes configurationdirectly contacts a source of electric or heat energy.
 10. Thedetachment mechanism of claim 1, wherein the detachment mechanismdirectly engages the vaso-occlusive device.
 11. The detachment mechanismof claim 1, wherein the detachment mechanism contacts a structureattached to the implantable device.
 12. A detachment mechanism adaptedto detachably engage a vaso-occlusive device, the detachment mechanismcomprising an element that changes configuration upon application ofelectrical current or heat; and means for applying electrical current orheat to the change the configuration of the element.
 13. Avaso-occlusive assembly comprising a vaso-occlusive device; a detachmentmechanism according to claim 1; and a source of electrical current or aheat source in contact with the detachment mechanism.
 14. Thevaso-occlusive assembly of claim 13, wherein the vaso-occlusive devicecomprises a helically wound vaso-occlusive coil.
 15. The vaso-occlusiveassembly of claim 13, further comprising a delivery mechanism.
 16. Thevaso-occlusive assembly of claim 15, wherein the delivery mechanismcomprises a stopper element.
 17. A vaso-occlusive assembly comprising avaso-occlusive device; a detachment mechanism according to claim 12; anda source of electrical current or a heat source in contact with thedetachment mechanism.
 18. A method of at least partially occluding ananeurysm, the method comprising the steps of introducing avaso-occlusive assembly according to claim 13, into the aneurysm,wherein the detachment mechanism engages the vaso-occlusive device; andchanging the configuration of the detachment mechanism by applying orremoving electrical current or thermal energy such that the detachingmechanism releases the vaso-occlusive device into the aneurysm.